Recently it has been proposed to add dispatch capabilities to Code Division Multiple Access (CDMA) communications systems, such as a cdma2000 communication system. Unlike the interconnect services provided by today's cellular systems, dispatch services have been traditionally provided by two-way radio systems. Such services allow a user to communicate in ways that are difficult or costly using today's cellular systems. Such services also allow for instant access by a mobile station originating a call to target mobile stations. For example, a dispatch group call service enables a user to communicate with a group of people simultaneously and instantaneously, typically by depressing a push-to-talk (PTT) key. Using a cellular system, such a call could not occur instantaneously since either telephone numbers would need to be dialed for a three-way call or arrangements would need to be made to setup a conference call. Likewise, a dispatch point to point call service enables a user to communicate with another user quickly and spontaneously, again typically by depressing a PTT key. This feature is ideal for two people who are working together but are unable to speak with one another directly such as two people working in concert but in different parts of a building. Where a wireless telephone call may be more appropriate for a conversation, short messages between two people as they work are better facilitated by the dispatch point to point call service.
Low delay is also a critical factor in any dispatch call. For example, setup delay that is acceptable for a typical interconnect voice call can be unacceptable for dispatch services which rely on a very fast connection being made to the called party. Accordingly, as noted above, dispatch services provide Instant Access call setup. However, a problem in implementing a dispatch system in a cellular communication system is that some telephones in the system will be dispatch enabled while legacy phones may not be so enabled. Furthermore, dispatch services permit only a single speaker to speak, or transmit, at a time while all others must receive, while typical interconnect systems allow each participant to concurrently transmit and receive. Users engaged in a dispatch communication session may find the dispatch service to be too constraining if the call turns into an extended conversation and may desire to switch to an interconnect communication session during the course of the call.
Therefore, a need exists for a method and apparatus that allows for fast interconnections required by dispatch users, that does not require that the user equipment be typical dispatch radiotelephones, and that permits users engaged in a dispatch communication session to switch to an interconnect communication session when the users so desire.